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Nous avons mené une expérience sur le terrain dans des champs de graminées pérennes pour déterminer les effets à long terme de la fertilisation annuelle par l’azote (112 kg de N ha-1), par le soufre (11 kg de S ha-1) et par le potassium (K) (40 kg de K ha-1) et l’application en une seule fois de chaux sur le rendement en matière sèche de fourrage (DMY) et les propriétés du sol [pH, carbone organique total (COT) et azote organique total (AOT), fraction légère du C organique (FLCO) et fraction légère du N organique (FLNO)] sur un sol loameux chernozémique gris foncé (boroll boralfique) à Canwood, dans le centre nord de la Saskatchewan, au Canada.
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Most soils in the Prairie Provinces of Canada are deficient in plant-available nitrogen (N), and many soils in the Parkland region also contain insufficient amounts of plant-available sulfur (S) for high crop production. A field experiment with perennial grass stand was conducted to determine the effects of long-term annual N (112 kg N ha-1), S (11 kg S ha-1) and potassium (K) (40 kg K ha-1) fertilization, and one-time lime application on forage dry matter yield (DMY) and soil properties [pH, total organic carbon (TOC) and N (TON), and light fraction organic C (LFOC) and N (LFON)] on a Dark Gray Chernozem (Boralfic Boroll) loam at Canwood in north-central Saskatchewan, Canada. The experiment had surface-broadcast annual treatments of no fertilizer (Nil), N, S, NS, and NSK fertilizers from 1980 to 2002, and one-time lime application in 1992 to bring soil pH to about 7. Application of N or S alone had only a little effect on DMY compared to unfertilized Nil treatment, while application of both NS together substantially increased DMY, and forage yield was further increased when K was also applied (NSK). The DMY following one-time liming was greater in limed plots than in unlimed plots for at least 10 years. Decline of soil pH by fertilization mainly happened in the 0-10 cm depth with N only, and in the 0-5 cm layer with NS treatment, whereas these treatments tended to increase soil pH in layers below 10 cm. One-time surface application of granular lime increased soil pH, mainly in the 0-5 cm layer, and the effect was maintained for at least 9 years. Mass of TOC, TON, LFOC, and LFON in different soil layers increased with combined applications of N and S fertilizers (NS), but the effect was much more pronounced in the 0-7.5 cm soil layer, and also varied with organic fraction. Light organic fractions were more responsive to applied NS than total organic fractions. The findings suggest that application of N and S together was effective in sustaining high forage yield and increasing C and N sequestration in a soil deficient in both N and S.
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